A chemical amplification resist composition is a pattern forming material that is capable of, upon exposure to far ultraviolet or other radiation, generating an acid at the exposed area and, by a reaction catalyzed by the acid, changing the solubility in a developer between the area having been exposed to actinic radiation and the nonexposed area to thereby attain pattern formation on a substrate.
In the use of a KrF excimer laser as an exposure light source, a resin whose fundamental skeleton consists of a poly(hydroxystyrene) exhibiting a low absorption mainly in the region of 248 nm is employed as a major component. Accordingly, there can be attained a high sensitivity, high resolving power and favorable pattern formation. Thus, a system superior to the conventional naphthoquinone diazide/novolak resin system is realized.
On the other hand, in the use of a light source of a further shorter wavelength, for example, an ArF excimer laser (193 nm) as an exposure light source, as the compounds having an aromatic group inherently exhibit a sharp absorption in the region of 193 nm, the above-mentioned chemical amplification system has not been satisfactory.
Therefore, resists for an ArF excimer laser containing a resin with an alicyclic hydrocarbon structure have been developed.
As for a photoacid generator which is a main component of a chemical amplification resist, triphenylsulfonium salt is generally known (see, for example, U.S. Pat. No. 6,548,221).
However, the acid generators above are unsatisfactory in many respects. Thus, there is a demand in the art for the development of a photosensitive composition that is enhanced in the sensitivity, resolution, pattern configuration, roughness characteristic, etc. through the improvement of such acid generators.
In particular, the roughness characteristic and resolution become serious in accordance with the reduction of pattern dimension. Therefore, in the field of, for example, the lithography using X-rays, electron beams or EUV, as the formation of a fine pattern of several tens of nanometers is targeted, the demand for especially high resolution and roughness characteristic is strong.
When use is made of a, light source emitting electron beams, X-rays, EUV or the like, the exposure is carried out in vacuum. This tends to cause low-boiling-point compounds, such as solvents, and resist materials decomposed by high energy to evaporate to thereby dirty the exposure apparatus. This outgas problem is becoming serious. In recent years, various researches have been made on the reduction of the outgas. Various proposals have been made, which include a proposal to inhibit the evaporation of low-molecular compounds by providing a top coat layer (see, for example, European Patent No. 1480078) and a proposal to add a radical trapping agent for the inhibition of polymer decomposition (see, for example, U.S. Pat. No. 6,680,157). For acid generators as well, an ingenuity for outgas reduction is demanded.
Furthermore, Japanese. Patent No. 3912761 proposes a positive photoresist composition for far-ultraviolet exposure which comprises a specified acid-decomposable resin and compound that is decomposed by an action of an acid to generate a sulfonic acid (hereinafter, referred to as sulfonic acid-generating compound) for the purpose of solving the problems of development defect, scumming, etc.
In Japanese. Patent No. 3912761, Paragraph 0016, there is a description that as the acid generated by the sulfonic acid-generating compound, one of high acid strength is preferred. Further, there is a description that a sulfonic acid containing an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group is preferred as the generated acid. In Paragraphs 0017 and 0018 of the reference, as preferred examples of the generated acids, there are mentioned the compounds of general formulae (1) to (5).